Low voltage percussion welder with auxiliary arc striking circuit



June 25-, 1957 5M T LOW VOLTAGE PERCUSSION WELDER WITH AUXILIARY ARCSTRIKING CIRCUIT Filed June 19, 1956 '/N VENTOR J. L. SMITH ATTORNEY 400VOLT SOURCE FIG. 2

54 VOLT SOURCE AND STORAGE CIRCUIT LOW VOLTAGE PERCUSSION WELDER WITHAUXILIARY ARC STRKKING cmcmr James L. Smith, Basking Ridge, N. 5.,assignor to Bell Telephone Laboratories, incorporated, New Yorlr, N. Y.,a corporation of New York Application June 19, 1956, Serial No. 592,386

6 Qlairns. (Cl. 219--95) This invention relates to a method andarrangement for use in percussion arc welding systems of the generaltype decsribed in detail in my copending joint application with W. S.Boyle, Serial No. 592,366, being filed concurrently with thisapplication. More particularly, it relates to the addition of anauxiliary high voltage, low current, storage circuit and charging sourcetherefor, to a low voltage (circa 50 volts), high current, percussionarc welding system, whereby the welding arc can be initiated at a muchgreater electrode separation. A substantially increased time is thenavailable in which to establish the high current amplitude through theare required to produce satisfactory welds. The inclusion of a largeresistor, in the order of 10 megohms, for example, in series with theauxiliary high voltage supply, substantially eliminates the hazard ofserious electrical shock to the person using the welder. The auxiliarycapacity likewise is of such low capacity that no substantial hazard ofshock is present.

As explained in detail in the above-mentioned copending application, ifa voltage in the order of only 50 volts is used an arc will not beinitiated until the electrodes have closed to a separation of probablyless than 5X10 inches. In view of the fact that the usual welding gunused in the type of system under consideration brings the electrodes, orpieces to be welded, together at a velocity in the order of 50 inchesper second, the normal time interval between the initiation of the arcand its extinction by closure of the electrodes will (at 50 volts) benormally only a fraction of a microsecond. In said copendingapplication, it was therefore suggested that one electrode be featheredor brought to a point so that when the arc was initiated the feather orpointed end would be burned back and a considerably greater additionaltime (circa 275 microseconds) thus gained before the arc wasextinguished by firm closure of the contacts.

Even with the best available types of noninductive leads, one of whichis illustrated and described in detail in my above-mentioned, joint,copending application, there will still be sufficient inductance in theleads and inherent inductance in the remaining components of the circuitin which the arc is established to delay the rise of current in the arcto the necessary amplitude by several microseconds. Usually a current inthe order of 400 amperes or more must be established to insure that asatisfactory weld will be obtained. This current must be maintained forat least a few microseconds to-form films of molten metal on each of thesurfaces which are to be welded together and to maintain the temperaturein the immediate vicinity of the weld until firm closure of theelectrodes has been effected. Cooling thereafter completes the weld.

In accordance with the present invention, it an auxiliary storagecircuit, of higher voltage but limited capacity, charged from a highervoltage but limited current source be associated with the 50 volt, highcapacity, storage circuit and a diode rectifier be inserted between thetwo to isolate the lower voltage storage circuit from that of 2,797,302Patented June 25, 1957 higher voltage, as will be described in detailhereinunder, an arc may be established at a much greater electrodeseparation. Assuming, for example, the higher voltage to be 400' vol-ts,an arc will be initiated between the electrodes by energy from the 490volt storage source at a separation in the order of at least X 10inches. Once initiated, the arc can be sustained by a relatively smallvoltage. For example, between clean copper electrodes the backelectromotive force generated in the arc will be in the order of 14volts. The above-mentioned diode switch then operates to permit the highcapacity 50 volt storage circuit to maintain the arc. Assuming oneelectrode to be a copper wire 20 mils in diameter, the high current fromthe 50 volt storage circuit will burn back this electrode several milsbefore the arc is extinguished by firm closure of the electrodes, sothat a total are duration in the order of to 2G0 microseconds or morewill be available in which to effect a strong, neat weld. The generalprocess is substantially as described in detail in my above-mentionedcopending joint application, except that since a relatively long featherneed not be burned ofi a somewhat shorter arc duration will sufiice.

For welding larger conductors to apparatus terminals, somewhat longerare duration intervals may be more suitable and can be obtained byincreasing the auxiliary voltage to 500 or even 600 volts so that thearc will be initiated at a still greater electrode separation. Thelastmentioned voltage represents about the upper limit at whichpresently available diode rectifiers can be expected to operatesatisfactorily. In addition, even a limited current source of highervoltage than 600 volts may involve some hazard of electrical shock topersonnel using the welding gun and thus defeat the principal objectivein using a main low voltage, energy storage circuit for arc welding inaccordance with the present application and applicants above-mentionedcopending joint application.

A principal object of the invention is to eliminate the necessity ofcarefully feathering an electrode in the process of percussion arcwelding of electrodes together where a main energy storage circuitcharged to a low voltage circa 50 volts) is to be employed.

Other and further objects, features, and advantages of the inventionwill become apparent during the course of the following description andfrom the appended claims.

An illustrative embodiment of the present invention is shown indiagrammatic schematic form in Fig. 1 of the accompanying drawing; and amodified low voltage, energy storage circuit for'use in the circuit ofFig. 1 is shown in Fig. 2.

In more detail in Fig. l of the accompanying drawing, the electrodesHand 14 represent, by way of example, a small conductor and a portion ofan apparatus terminal, respectively, which are to be are Welded to forma good electrical and strong, neat, mechanical connection therebetween.

Electrodes 12 and 14 are held in a percussion welding gun, not shown indetail but represented diagrammatically by the dash-line block 10. Gun10 can be, for example, a trigger operated mechanism of the typeillustrated and described in detail in the copending application of A.L. Quinlan, Serial No. 581,074, filed April 27, 1956. Alternatively, itcan be substantially as described in United States Patent 2,184,627,granted December 26, 1939, to G. W. Watson. The functions of the gun areto throw the switch 20 from its off position 16 to its on position 18and simultaneously to bring the electrodes 12 and 14 together at anappreciable velocity such, for example, as a velocity of from 10 to 50inches per second.

With switch 20 in its off or charging position, high voltage source 22charges capacitor 28 to its own voltage through the circuit includingresistors 24 and 30 and 3 ground. Resistor 24 functions to limit thecurrent which can be drawn from voltage source 22 to a value such thatthe hazard of serious electrical shock to a person using the welder issubstantially eliminated. Resistor 30 functions to critically damp thecircuit including capacitor 28 so that oscillations cannot be set up.

Diode rectifier 26, which can, for example, be a high power, siliconrectifier, of the type disclosed and claimed in the copendingapplication of M. B. Prince, Serial No. 503,299, filed April 22, 1955,serves to isolate the 54 volt source and energy storage circuit 34 fromthe high voltage source 22 and its associated storage circuit.

The 54 volt source and energy storage circuit 34, having terminals 36and 38, can be substantially identical with those disclosed, describedin detail, and claimed in my above-mentioned copending jointapplication, except that since, as described hereinabove, a somewhatshorter over-all arc duration interval is contemplated in connectionwith the arrangements of the present invention, the transmission line orladder network portion of the storage circuit of my copending jointapplication can, for the purposes of the present invention, comprisefewer sections. More specifically, as shown in Fig. 2, only three seriesinductors 46 and three shunt capacitors 48 (instead of five each, as perthe copending joint application) need be employed for use inarrangements of the present invention. As for the copending jointapplication, source 44 may have a voltage of 54 volts, resistor 50 mayhave a resistance of 1000 ohms, capacitor 40 may have a capacity of 750microfarads, resistor 42 may have a resistance of .04 ohm, each ofcapacitors 48 may have a capacity of 200 microfarads, and each ofinductors 46 may have an inductance of 8 microhenries.

correspondingly in Fig. 1, described above, where source 22 has avoltage of 400 volts, resistor 24 may have a resistance in the order of10 megohms, resistor 30 may have a resistance of approximately ohms, andcapacitor 28 may have a capacity of 10,000 micromicrofarads.

When an arc is initiated between electrodes 12 and 14 by discharge ofcapacitor 28, the back electromotive force generated in such a shortare, between, for example, clean copper electrodes, will be in the orderof 14 volts. Energy from the storage circuit 34, flowing through dioderectifier 26, can then sustain the arc and complete the welding process.The general considerations involved after the initiation of the are aresubstantially the same as for arrangements of my above mentionedcopending application, except that since a relatively long feather neednot be burned off one of the electrodes the actual arcing interval maybe somewhat less and the sustained surge of power from the laddertypestorage network can therefore have a somewhat shorter duration so as toterminate within 100 microseconds or so after firm closure of theelectrodes and the consequent extinction of the arc has occurred.

Numerous and varied arrangements within the spirit and scope of theprinciples of the present invention will readily occur to those skilledin the art. No attempt to exhaustively cover all such arrangements hashere been made.

What is claimed is:

l. A percussion arc welding system which includes, in combination a pairof electrodes to be welded together, an energy storage circuit whichincludes a high voltage, low capacity portion, a low voltage, highcapacity portion and a diode rectifier interposed between said portionsto isolate the low voltage from the high voltage portion and to switchfrom one to the other as the high voltage portion is discharged, lowinductance means interconnecting both said portions to said electrodesand means for bringing said electrodes together at an appreciablevelocity whereby an arc will be initiated at a substantial electrodeseparation, determined by the high voltage portion of the energy storagecircuit, and sustained by the low voltage portion of said storagecircuit until the arc is extinguished by firm closure of saidelectrodes.

2. An energy storage circuit for a percussion welding system, saidcircuit including a high voltage, limited capacity portion and a lowvoltage, high capacity portion, the two being connected in parallel, adiode rectifier included between said high voltage and low voltageportions to isolate the latter from the former portion and lowinductance leads for connecting said storage circuits to a pair ofelectrodes to be welded together during the welding interval.

3. An energy storage circuit for a percussion arc welding system of thetype which includes, as the main source of welding power, a highcapacity storage circuit and means to charge said circuit to a voltagesubstantially less than volts, an auxiliary source of welding powercomprising a low capacity storage circuit, means for charging said lowcapacity storage circuit to a voltage of several hundred volts, saidmeans including in series therewith a resistor of several megohms, andmeans connecting said main and said auxiliary sources in parallel, saidlast-mentioned means including a high power rectifier connected toisolate said main source from said auxiliary source.

4. A circuit as defined in claim 3 and a resistor connected in serieswith said low capacity storage circuit to inhibit oscillations in saidcircuit.

5. A circuit as defined in claim 4 and low inductance means to connectsaid storage circuits to electrodes to be welded together.

6. An energy storage circuit comprising a high capacity portion, meansfor charging said portion to a voltage of less than 100 volts, a lowcapacity portion, means for charging said low capacity portion to avoltage of several hundred volts, said last-mentioned means including inseries a resistor of several megohms, a rectifier interconnecting saidtwo portions and inhibiting the transfer of energy from said lowcapacity to said high capacity portion while permitting energy transferin the reverse direction and resistive means in series with said lowcapacity portion to inhibit oscillation in said portion.

References Cited in the file of this patent UNITED STATES PATENTS1,373,054 Chubb Mar. 29, 1921

